AGGLUTININS 55 



Nature of the Agglutinins, and of the Agglutina- 

 tion Reaction. The agglutinins are fairly resistant 

 substances which withstand heating to 60 C., and 

 lose their power only on heating to 65 C. It is pos- 

 sible, therefore, to make a serum bacteriolytically in- 

 active by heating to 55C., and still preserve its agglu- 

 tinating power. It has been found that agglutinins 

 when heated may keep the property of uniting 

 with bacteria, although they lose the property of 

 agglutinating them. To explain this fact, Ehrlich 

 supposes that agglutinins possess two groups, a 

 haptophore group, effecting the specific union with 

 the cell, and an ergophore group, which effects the 

 clumping. He supposes further that under the con- 

 ditions mentioned the agglutinin loses its aggluti- 

 nating group but keep* its combining group. Such 

 a modified agglutinin, Ehrlich calls an agglutinoid, 

 just as toxins which have lost their toxophore 

 groups are called toxoids. The nature of agglutinoid, 

 however, is still very obscure. In fact, as we shall 

 presently see, the opponents of the Ehrlich school 

 refuse to believe in the existence of agglutinoids. 

 It has occasionally been observed that agglutination 

 is absent in concentrated serum, and present in dilute 

 serum. This zone of no agglutination, preceding that 

 of agglutination, is often spoken of as the pro zone 

 and was first described by Eisenberg and Volk. Ac- 

 cording to Ehrlich it is due to the presence in the 

 senim of agglutinoids. These are assumed to possess 

 higher affinity for the bacteria than do the agglutinins 



